The present invention generally relates to methods and systems for providing cardiac pacing therapy. More particularly, the invention concerns methods and implantable stimulation devices to detect conditions that might give rise to orthostatic hypotension and/or syncope and provide pacing-based cardiac therapies aimed at reducing the effects of orthostatic hypotension and/or syncope.
When an individual changes from a horizontal or supine position to a sitting or standing position, the cardiovascular system must make frequent and rapid adjustments to blood pressure and heart rate. When such adjustments are not accomplished, orthostatic hypotension occurs. Orthostasis means upright posture, and hypotension means low blood pressure. Thus, orthostatic hypotension describes the effects caused by low blood pressure when changing from a lying to upright position. Orthostatic hypotension is defined as a decrease of at least 20 mm Hg in systolic blood pressure when an individual moves from the supine to upright position.
The symptoms of orthostatic hypotension include dizziness, faintness, or lightheadedness that appear when standing. Other symptoms that often accompany orthostatic hypotension include chest pain, trouble holding urine, impotence, and dry skin from loss of sweating. Some patients with severe orthostatic hypotension are severely incapacitated.
In addition to orthostatic hypotension, a similar condition that may occur when a patient changes from a supine to upright position is syncope. Syncope describes the effect of temporary impairment of blood circulation to a part of the body. Patients with severe orthostatic hypotension often experience syncope for one to two minutes after sitting up in bed, or after standing.
Two common forms of syncope include vasovagal syncope and carotid sinus syncope. Vasovagal syncope is a condition marked by a sudden drop in heart rate and blood pressure, resulting in fainting. Carotid sinus syncope occurs when reduced blood pressure results in impaired blood flow to the brain, causing brief unconsciousness or fainting. Both vasovagal syncope and carotid sinus syncope are not only unpleasant for a patient, but also potentially dangerous, as fainting may lead to injuries from falls.
This invention arose out of concerns associated with accurately detecting a patient""s position changes and timely administering therapy to reduce any effects of orthostatic hypotension and/or syncope.
An implantable cardiac stimulation device is programmed to administer pacing therapy in response to a change in a patient""s position and a drop in blood pressure. The pacing therapy is an increase in the cardiac pacing rate to counteract effects of orthostatic hypotension and/or syncope.
In the described implementation, the cardiac stimulation device is equipped with a position sensor to sense a position parameter indicative of when a patient changes from a supine position to an upright position, such as when moving from a sleeping or reclined posture to a sitting or standing posture. One example of a position sensor is a 3D accelerometer that detects movement in three dimensions.
The cardiac stimulation device is further equipped with a pressure sensor to sense a pressure parameter indicative of a patient""s blood pressure. The pressure sensor may be configured to sense pressure directly (e.g., a lead-based pressure sensor that senses pulse pressure or a can-based oxygen sensor) or indirectly (e.g., a photoplethesmic sensor that detects changes in tissue that can be correlated to pressure changes).
The cardiac stimulation device includes a processor operably coupled to the position sensor and the pressure sensor. The processor is programmed to determine when to administer cardiac pacing therapy to the patient based on the position parameter and the pressure parameter. For instance, the processor decides to apply an increased pacing rate effective to treat orthostatic hypotension when the patient experiences both (1) a change in position from a supine position to an upright position and (2) a drop in blood pressure below a predefined threshold.
The processor may further be programmed to apply therapy for treating vasovagal syncope. This therapy is applied when the patient experiences a rapid drop in blood pressure below a threshold level. A position sensor may be used to confirm the onset of vasovagal syncope by detecting that the patient is in a vertical position (e.g., standing or sitting up) and hence should not be experiencing a rapid drop of blood pressure.
In both treatments, the processor is programmed to continue monitoring the pressure sensor. When the patient""s pressure rises back above another threshold (which may or may not be the same as the first threshold), the pacing therapy is systematically removed to slowly decay the pacing rate from the increased therapy rate back to the base rate of the patient prior to therapy.